Signaling system



Feb. 16 ,1926

C. W. GREEN SIGNALING SYSTEM Filed Dec. 17, 1921 Rv m s g} hwm/ar: E I Char/e5 [4/ Gwen l mented lFelo. id "Q26.

CHARLES WILLIAM GREEN, OF NEW YORK, N. Y., ASSIGNOI} TO WESTERN ELECTRIC COMEANY, INCORZORATED, 0F NEW YORK, N. Y., A CORPORATION OF NEW YORK.

SIGNALING SE2 STEM.

Application filed December 17, 1921. Serial No. 523,008.

To all 107mm it may concern:

Be it known that I; {ll-Limits lVILLL-iiit Guzman, a citizen of the United States. residing at New York city, in the county of liionx, State of New York, have invented certain new and useful Improvements in Signaling Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to signaling systerns and more particularly to repeating systems in which signals of dilferen types or frequencies are desired. to be repeated with diil'erent degrees of amplification.

The preferred form of this invention will be hereinafter descri ed in detail in connection with a two-way telephone repeater ofthe relayed ringing type in which a source of calling currents is connected to one line section when incoming calling currents are received from the other line. Such a repeating system has sometimes been found to have such a degree of amplification for ringing currents that incoming ringing currents in one line section would pas;- through the repeater and cause the false operation of the ringing current responsive means associated with the other line section,a result which is, of course, undesirable.

In accordance with this invention the false operation of the ringing responsive means is prevented by providing means for ieducing the amplification of the ringing currents to such an extent that the currents of the ringing frequency which tend to pass through the repeater, are of negligible or practically Zero amplitude, While still maintaining the desired repeater gain characteristic for those frequencies of importance in speed. This means preferably comprises a series resonant circuit connected across the input leads of the repeater or across the midpoiuts of eachthree-winding transformer and tuned to the frequency it is desired to suppress; or it may comprise an anti resonant circuit in series with the input leads and tuned to that frequency. If the ringing; currents are of Bicycles for example, this resonant circuit, shouh'l be tuned to that frequency. This invention. in th case above described, is also preferably employed in connection with the usual series condensers present in the line for reducing the intensity of the ringing currents prior to in'ipressing them on the tuned circuit and the repeater. It has been found that the use of this resonant circuit does not appreciably interfere with the repeater gain correcting means such as that described, for example, in Casper application Serial No. 366,581, tiled Larch 17, 1920, which has heroine Patent 1,530,6l8, so that the simultaneous use of the correcting means of this "mention and that of Casper producer a practically flat repcatcrgain characteristic from 200 or 300 cycles to 2000 cycles, with a negligible repeater gain for 135 cycle currents.

1 his invention will be better understood by reference to the following detailed description taken in connection with the ac companying drawing. in which Fig. 1 illustrates schematically this invention embodied in a 22 type telephone repeater circuit cmplojving relayed ringing; and 1 19;. 2 is a modification thereof. 7

The signaling system disclosed in Fig. 1 comprises two line sections 10 and 11 between which may be connected a 22 type re peater circuit comprising an amphticr 12 for amplifying currents from line section l l and amplifier ill for amplifying currents from line section 11. The amplii'ying elements shown are of the \vell'knou'n vacuum tube type and it is not thought necessary to gie herein a detailed description of their method of operation.

7 Line section 10 is shown as terminating in a threcuvindiug transformer Li and an appropriate lmlancin; network 15, while line section 11 is terminated in a similar threewindinp; transformer 16 and a balancing nctn'orh 17. The midpoints of the throw winding transformer l-l are connected to the nput terminals of the amplifier 3 through leads which include a gain adjusting potentiometer 1S and an input transformer 19. Similarly, the midpoints of-"thc three- Winditlg transforn'ier 16 are connected to the input terminals of amplifier 13 through leads including a corresponding grain adjusting potentiometer and input transformer 2 The output terminals of each of the amplifiers are connected through a Camp bell Wave filter to the third winding of one of the ,chree-winding transformers. From this brief description, it will be apparent to those skilled in the art that incoming signalling currents, such as speech currents from line section 10 will be impressed through in put transformer 19 upon amplifiez i2 thereupon the other line section 11. tiimilarly, any incoming speech currents from line sec tion 11 will be received by the amplifier 13 through the intermediary of input trans-- tornier 2i and will be amplified before being impressed on line section 10.

In case it is desired to relay the ringing or calling currents of the telephone system around the repeaters 12 and 13 instead of allowing them to be amplified in the same manner as speech currents, a relayed ring; ing arrangement may be employed, such. for example, as that shown in the Toomcy Patent No. 1,36-l,'150, issued January 4,1921, This relayed ringing arrangen'ient coinprises, in brief, a ringing responsive relay normally connected in shunt to line section 10. Incoming ringing currents from line section 10 will cause the energization of relay25 and by obvious circuits will deenergize relay 26 and energize relays 27 and 28. The energization of relay 28 breaks the connection between the three-winding transformer 1G and line section 11, and connects instead, a suitable source of ringing cur rents to line section ll. In a similar manner, incoming ringing currents from line section 11 cause the encrgization of an alternating current relay 30 which produces successively by obvious circuits, the deen ergization of relay 31 and the energization of relays 32 and 33. Relay 33 on being energized, connects a suitable source of ringing current through the line section 10 while disconnecting the line section from the repeater. Relays 30 and 33 in opcrating,also serve to connect artificial networks 35 and 36 to the line side of the three-winding transformers in order to prevent the repeater circuit from being unbalanced during the ringing operation.

As described in the above mentioned Casper patent and the lVhiting application Serial No. d06,861, filed August 30, 1920, which has become Patent 1,530,633, it has sometimes been found preferable to provide means in the repeater circuit for giving the vacuum tube amplifier substantially a flat repeater gain characteristic. over the entire range of frequencies of importance in speech. This result may be obtained by adjusting the transformer leakage to overcome transformer capacity eti'ects and the internal capacity of the associated repeater and by including a. resistance 40 and a capacity 39 of the proper values in circuit with the transformer. This arrangement,

masses I however, while giving the desiried fiat repeater gain characteristic over the range of frequencies of importance in speech, also serves to increase quite appreciably the amplification of the repeater of those frequencies below the speech range such as those normally used for ringing or calling curby being ampliliel before being impressed rents, namely, ofthe order of 135 cycles.

Heretofore, 1n repeater circuits of the re layed ringingtype in which it is desired to prevent the amplification of the ringing currents, ithas been found sufiicient for repeaters with low gains at ringing frequencies to merely include serially in each line section condensers such as those shown as l1, and i4 of the drawing, of such values asto have the necessary high impedance for the ringing currents ivhile offering negligible impedance to the transmission of speech currents. This simple expedient, however, has not been found sufiicient 'lor repeater circuits employing the improved means above described for giving the amplitier a fiat gain characteristic curve. Due

to the large'gain of the repeater for 135 cycles, ringing currents of suflicient strength occur in the output circuit of each repeater to frequently cause the false operation of the ringing responsive relay associated with the other line section,a result.

which is, of course, highly undesirable.

in accordance with this invention, the gain of the repeater for ringing frequencies has been reduced and the false operation of the ringing responsive relay is prevented by the connection across the input leads of each half of the repeater circuit of a series resonant circuit comprising an inductance and a capacity 46 of such values as to maintain the input leads at substantially the same potential for the "frequency of the ringing currents while n'laintaining the de sired potential (inference therebctwcen for the ircrpiencics of importance in speech.

"lhe use of this series resonant circuit has beenfll'riund particularly advantageous for the reason that its use n'oduces no substantialnalterationin the shape of the repeater gain characteristic curve "tor those trcqucncies greater than 135 cycles. For example, in one use, a telephone repeater had asub stantially constant gain of 23 miles for all frequencies between 135 cycles and 2000 cycles in the case 'as not included. lVhen the shunt circuit was included, the repeater had a substantially constant gain of 22 miles for frequencies between 300 and 2000 cycles, while it had a gain of less than a. mile for 135 cycles.

If desired, the correcting network for suppressing. the signaling currents may comprise an anti-resonant circuit connected in series with the input leads and tuned to the signaling frequency. This arrangement wherethe shunt circuit 1 Ill revenue is shown in Fig. 2 where elements l8 and 49 constitute the anti-resonant circuit In order to keep the circuit symmetrical, it will generally be preferable to duplicate elements 48 and all) in the other side of the line as shown by elements 50 and 51.

In general, however, it will be found preferable to employ the series resonant circuit for the reason that it does not require the breaking of the input leads of the rcpeater but may be connected or disconnected at will without disturbing the operation of the repeater when it is desired to change the repeater from a through-ringing type to a relayed-ringing type or vice verse.

I Another advantage derived from the use of the resonant circuit of this invention is that it aids in obtaining a satisfactory balance between the artificial balancing network for example and the associated line 10. Line 10 when composited for example 'will have apparatus associated. therewith which is difficult to balance because its impedance changes rapidlyfor frequencies in the neighborhood or 100 cycles. The reduction of the repeater gain for 135 cycles due to the resonant circuit obviates the necessity for as accurate a balance between line 10 and artificial line 15 for frequencies of the order of 100 cycles for frequencies in thespeech range.

When the series resonant circuit is employed, the inducta ce a5 should be made as small as is consistent with good quality transmission in order to reduce the l). C. resistance of the shunt circuit to a small value. (7n the other hand, inductance 48 should be I made as large as is consistent with good quality transmission in order to make the impedance of the circuit as high as possible for the resonant frequency. It has been found, however, that if clement 4:5 is cecreascd beyond a certain value and element 18 increased beyond a certain value that the elements produce an undesirable modification of the repeater gain charactertistic for frequencies near the upper range essential to speech. lV hen the frequency to be suppressed is in the neighborhood of 135 cycles, element should preferably have a value of approximately one hen ry and element l8 approximately two henries.

Although this invention has been described above in connection with means for giving a vacuum tube repeater a substantially constant gain over the entire range of frequencies 0t importance in speech, it is obvious that this invention is not limited in its application to systems employing such means.

t will also be apparent to those skilled in the art that this invention can be advantageously used m si 'nalmg systems widely different from the telephone repeater system desired to supdescribed above wherein it is whue press signals or"; a certain frequency permitting the through transmission of signals of other frequencies or types.

"What is claimed is: i

1. In combination, two line sections, a repeater circuit therebetween, a repeater ele ment therein, a transformer in said circuit, means associated with said transformer for causing said element to have a substantially constant amplification over a wide range of frequencies which it is desired to transmit through said repeater, and means for preventing the passage of an undesired frequency through said repeater circuit without appreciably effecting the ampl cation cha *acteristic of said element for said range of frequencies comprising an inductance and a capacity r sonating at the undesired frequency.

2. In combination, two line sections, a repeater circuit therebetween comprising an amplifying element and a transformer, means associated with said transformer for causing said repeater to have a substantially constant amplification for the entire range (it-frequencies of importance in speech, and means for preventing the passage of an undesired ringing current frequency through said repeater circuit without appreciably effecting the amplification characteristic of said repeater for said range of frequencies, said means cou'lprising a path effectively in shuntto a winding of said transformer and including an inductance and a capacity serially connected with respect to each other.

3. In combination, an amplifying repeater, means for giving said repeater :1 substantially constant amplification for all frequencies between 300 cycles and 2000 cycles, and means for making said repeater have an amplification of substantially zero for frequencies in the neighborhood of 135 cycles.

a. in combination, two line sections over which voice currents and ringing currents are adapted to pars,alink circuit comprising an amplifying repeater for interconnecting said lines, means for causing said repeater to have a substantially constant amplifica tion characteristic over a wide range of voice frequencies, and resonating means for preventing the passage of ringing current to said reptater while maintaining substantially constant the amplification characteristic of said repeater for the voice currents.

A. two-way repeating system comprising two uni-directionally t'ansmittiug electric space discharge wave amplifiers, each capable of transmitting the frequencies of a given frequency band with substantially uniform amplification over said frequency band, two circuits, one having an impedance more difiicult to balance for frequencies near a given frequency in the neighborhood of said hand than for other treouency regions, means, including nnpedance balancin networks for said circuits, connecting am amplifiers for transmitting in opposite 'diz'ec tions between said circuits, and circuits, each including inductance and capacitytuned to said given #frequency and so connected to said last mentioned means as to be capable of substantial discrimination against waves of said given frequency compared t0 Waves of neighboring frequencies, both as regards iine-to-line fi'ansmission and as regards transmission around ihe 100p con'lprising the 10 amplifiers.

In witnesswhereof, I hereunto subscribe my name this 14th dayof December, A. I). e 1921.

CHARLES WILLIAM GREEN. 

